What's the difference between sigma 8mm lens and Nikon 16mm fisheye, and a Nikon 14mm wide angle lens?

Theoretically, Nikon 16mm fisheye, and a Nikon 14mm wide angle can be applied to our software, but won't do the same good job as the Sigma lens. The problems with them are:

• Firstly, they can only be used in 135 frame film camera and DSLR of full frame if you want to make use of our software to stitch images; 
• Secondly, we haven't tested them yet, so we couldn't guarantee the usage; 
• Thirdly, if they were compatible with our panorama software, you have to take more than 8 pictures to make a panorama. If you use a sigma 8mm lens, you only need to take 4 or less pictures to make a panorama, meanwhile the sigma 8mm lens can be compatible with almost all the DSLR.